Method and system for engine temperature control

Abstract

Methods and systems are provided to improve engine temperature control. Cylinders scheduled for deactivation may have their exhaust retained in the cylinder by holding an exhaust valve closed on the preceding firing cycle. In this way soot emissions on reactivation are reduced.

The invention claimed is: 
     
       1. A method for an engine, comprising:
 selecting a first cylinder for deactivation; and 
 on an engine cycle immediately preceding the deactivation, maintaining an exhaust valve of the selected cylinder closed during an exhaust stroke of the cylinder; 
 selecting a second, different cylinder for deactivation, and 
 operating the second cylinder in a first mode with an intake valve opening during an intake stroke, a fuel injector deactivated, deactivated spark, and with an exhaust valve opening during an exhaust stroke; 
 operating the second cylinder in a second mode with the intake valve opening during the intake stroke, the fuel injector activated, deactivated spark, and with the exhaust valve opening during the exhaust stroke; 
 operating the second cylinder in a third mode with the intake valve opening during the intake stroke or a compression stroke, the fuel injector activated and fuel delivered during the compression stroke, deactivated spark, and with the exhaust valve opening during the exhaust stroke; 
 operating the second cylinder in a fourth mode with the intake valve opening during the intake stroke, the fuel injector activated, spark delayed to the exhaust stroke, and with the exhaust valve opening during the exhaust stroke; and 
 selecting one of the modes based on exhaust catalyst temperature. 
 
     
     
       2. The method of  claim 1 , wherein the selecting a cylinder for deactivation is responsive to a drop in engine load. 
     
     
       3. The method of  claim 1 , wherein, during the selecting, an exhaust temperature is higher than a threshold temperature. 
     
     
       4. The method of  claim 1 , further comprising, during reactivation of the selected first cylinder, opening the exhaust valve before opening an intake valve to release trapped exhaust gases before inducting air. 
     
     
       5. The method of  claim 1 , wherein opening the exhaust valve includes opening the exhaust valve during an exhaust stroke of an engine cycle immediately preceding the reactivation. 
     
     
       6. The method of  claim 1 , further comprising deactivating the selected first cylinder for a number of engine cycles, wherein the maintaining an exhaust valve of the selected first cylinder closed is responsive to the number of engine cycles being higher than a threshold number. 
     
     
       7. The method of  claim 6 , wherein the threshold number is based on one or more of an engine coolant temperature, an ambient temperature, and a cylinder temperature, the threshold number decreased as any of the engine coolant temperature, the ambient temperature, and the cylinder temperature decreases. 
     
     
       8. A method for an engine, comprising:
 deactivating a cylinder pattern of individual cylinder mechanisms, the cylinder pattern including a first deactivated cylinder and a second active cylinder, wherein in response to a command for deactivation of the first cylinder, and further based on an engine temperature, an exhaust valve of the first cylinder is held closed on an exhaust stroke of an engine cycle immediately preceding the deactivation of the first cylinder; and 
 in response to the engine temperature being below a threshold, operating a third cylinder with a rich fuel injection delivered during a compression stroke and spark deactivated while operating a fourth cylinder with a lean fuel injection delivered during an intake stroke and spark deactivated. 
 
     
     
       9. The method of  claim 8 , wherein the exhaust valve of the first cylinder held closed based on engine temperature includes the exhaust valve held closed in response to the engine temperature being lower than the threshold. 
     
     
       10. The method of  claim 9 , wherein the cylinder pattern further includes a number of engine cycles over which the first cylinder is maintained deactivated, the method further comprising reactivating the first cylinder after the number of engine cycles. 
     
     
       11. The method of  claim 10 , wherein the engine temperature is an estimated engine temperature or an expected engine temperature, the expected engine temperature including a temperature of the engine or an engine component expected at the reactivating. 
     
     
       12. The method of  claim 10 , further comprising, during the reactivating, opening the exhaust valve of the first cylinder before opening an intake valve of the first cylinder to release trapped exhaust gases before inducting air into the first cylinder. 
     
     
       13. An engine system, comprising:
 an engine having a plurality of cylinders, each cylinder including an intake valve and an exhaust valve; 
 a deactivation mechanism for deactivating at least one of the intake valve and the exhaust valve of one of the plurality of cylinders; 
 a temperature sensor for estimating an engine temperature; and 
 a controller configured with computer-readable instructions stored on non-transitory memory for:
 selecting one of the plurality of cylinders for deactivation based on engine load; and 
 on a first engine cycle, opening the intake valve of each of the plurality of engine cylinders during respective intake strokes, holding the exhaust valve of the one of the plurality of cylinders closed during an exhaust stroke while opening the exhaust valve of remaining cylinders during respective exhaust strokes; and 
 on a second engine cycle, immediately following the first engine cycle, deactivating the intake valve and the exhaust valve of the one of the plurality of cylinders while maintaining remaining cylinders active; 
 wherein the holding the exhaust valve of the one of the plurality of cylinders closed during the exhaust stroke is responsive to the engine temperature being lower than a threshold, the method further comprising operating at least one of the remaining cylinders with spark active and fuel enrichment while operating at least another of the remaining cylinders with spark active and fuel enleanment to raise the engine temperature above the threshold. 
 
 
     
     
       14. The system of  claim 13 , further comprising operating one or more of the remaining cylinders with spark timing delayed into an exhaust stroke to raise the engine temperature above the threshold. 
     
     
       15. The system of  claim 13 , further comprising, on a third engine cycle, reactivating the exhaust valve of the one of the plurality of cylinders and opening the exhaust valve during an exhaust stroke, and during a fourth engine cycle immediately following the third engine cycle, reactivating the intake valve of the one of the plurality of cylinders and opening the intake valve during an intake stroke.